Slab surfacing machine



May 30, 1961 Filed July l5, 1958 L. H. KNOST SLAB SURFACING MACHINE 5 Sheets-Sheet 1 May 30, 1961 l.. H. KNosT 2,985,989

SLAB SURFACING MACHINE Filed July l5, 1958 5 Sheets-Sheet 2 May 30, 1961 I.. H. KNosT I 2,985,989

SLAB SURFACING MACHINE Filed July l5, 1958 5 Sheets-SheeIl 3 /0 I I I I I I I I I I I "9 l i I I I I JZL Q0 59 l I I I L h I I II iI I I I I I I I I I I I I I I I l I INVENTOR: .ZZQrycZ/bfzos* May 30, 1961 L. H. KNosT 2,985,989A SLAB suRFAcING MACHINE Filed July 15, 1958 May 30, 1961 H. KNosT 2,985,989

SLAB SURFACING MACHINE Filed July l5, 1958 5 Sheets-5h68?l 5 ZZ H255 BY. @y i205 mi if 2,985,989 SLAB SURFACING MACHINE Lloyd H. Knast, L. H. Knast C0., P.0. Box 415, Carthage, M0. Filed July 15, 1958, Ser. No. 748,741 21 Claims. (Cl. 51-55) This invention relates to a surface finishing machine for various kinds of hard materials.

More specifically, the invention is directed to a machine for finishing a surface area of a slab composed of a material such as marble, granite, terrazzo, glass and of other analogous substances. Thus, while various other work pieces or slab materials may readily be worked upon with a machine of this character, the subject matter hereinafter will generally refer to the slab material such as marble for the sake of convenience and consistency of description.

Various laborious hand finishing methods have been used over the past years to finish surfaces on slab materials and such methods are still resorted to in some instances. To reduce the tedious and time consuming ways of manually finishing hard slab materials, various mechanical methods have been developed to provide means to surface finish slab materials.

The mechanical systems developed are fundamentally such as to provide mechanisms that guide grinding wheels over and seated upon a slab of stone, marble, granite or the like. Such mechanisms employ what is known as floating types of grinding heads which make no allowances whatever for the irregular surface contours presented by a particular slab that is being worked upon. The heads actually contour finish the slabs.

When slabs of stone or mable, as an example, are cut at the quarries by gang saws, the surface face areas are not at all true and level, but a slab surface will have low spots and high spots over Various portions of the faces thereof. With a floating head type of a grinding spindle, the grinding wheel is made to engage upon the surface of such a slab for the surface finishing and/or polishing operation of a face thereof. As the slab passes under the grinding wheel, the wheel will follow the adjacent surface contour of the slab whether convex or concave as developed from the previous gang saw operation. The final outcome is a wavey or undulant final surface on the finished slab. No uniformity exists in the slab thickness and the finished surface is not a true, flat or coplanar area.

One of the objects of the present invention is to provide a slab surfacing machine that does not follow the undulations of the surface of a slab of material, but a machine that is constructed and arranged to edgewise shave or grind off a fixed increment of material from a slab to level off the slab top along a given thickness in relation to the underside ofthe slab. Thus high points and low points on a slab surface have no effect on the operative cutting elevations of the grinding wheels.

In other words, the grinding heads are set to cut a true horizontal swath of material from one surface of the slab that will provide a gauge cut of determinable character, taking off the excess slab material at the convex areas and the lesser but appreciable slab material at the concave areas of the slab. This is considered a new and novel solution to a hitherto uncontrolled and unpredictable slab surface finishing practice.

It is another of the objects of the present machine to provide an efiicient assembly of coacting mechanisms that will function consistently to produce a given or predetermined true and level surface finish on a slab material and at the same time exercise a high degree of control that will provide such a slab with a determinable maximum thicknessV and accurate level surface finish when completed.

Another object of this invention is to provide a finish- 2,985,989 Patented May 30, 1,961

ing mechanism to smoothly surface a slab material under certain controlled compound motions of Voriented grinding mechanisms which under operation cooperatively act to quickly and finely mill off selectedcoplanar increments of surface material from a slab to obtain a true high gloss finish on the work piece.

As another object, the machine providesV means to manipulate and bodily actuate a battery of grinding spindles together in'concerted unison with their associated grinding or polishing wheels and in an oscillatory fashion in a transverse direction across a slab of materialwhile the latter is being moved rectilinearly over a roller hedor other instrumentality supporting such a slab.

Another object is to provide a slab finishing machine with 'mechanism including multiple grinding heads having the finishing wheels thereof closely and adjacently positioned whereby, under oscillation, the action provided produces a considerable percentage of overlap of the wheel action upon common slab areas that are serviced by such adjacently positioned wheels.

Other objects of this invention reside in the construction of the novel arrangement of the various mechanisms to obtain the close tolerance adjustments that benefit the consistent end results obtained; the manner of the positive level support of the grinding heads and the incorporated micrometer manualadjustment means of the individual heads; the oscillatory mechanism employed to actuate the battery of heads; and in the combinations of mechanisms f that together produce the finished work pieces as will hereinafter be described with greater particularity.

All other objects andadvantages relating to the material slab finishing machine of the present invention will hereinafter appear in or become evident from the following more detailed description of the machine having reference to the drawings disclosing a preferred construction of the machine and forming a part of this specification.

In the drawings:

Fig. l is a side elevational View of a slab material surfacing and finishing machine incorporating the principles of the present inventive concept;

Fig. 2 is a front en d elevational View of the machine as the same appears when viewed from the right hand end of Fig. l;

Fig. 3 is a Afragmentary plan view of the grinding head assembly section of the machine;

Fig. 4 is a vertical cross sectional view of one of the identical spindle grinding head assemblies as such apparatus appears when viewed along the plane of the line 4--4 in Fig. 2; Y

Fig.V 5 is a bottom plan view of a fragmentary portion of the grinding wheel of the head shown in Fig. 4;

Fig. 6 is an enlarged radial sectional view of a portion of the grinding wheel per se to illustrate certain structural details thereof; and

Fig. 7 is a diagrammatic plan View of the grinding mechanisms of the present invention to better illustrate the oscillatory action and operation thereof, this view omitting the center grinding heads for the sake of clarity, but showing the two outer end heads as being on the same center to center spacing that exists between the respective` multiple heads of this apparatus.

While the following description will be directed to the embodiment illustrated in the drawings, certain deviations in the combination of elementsemployed are considered permissible that will not depart from the general fundamental'scope of the invention. As one example, while only four grinding units are shown in the drawings, this number may be readily increased Vto any numberund'er various conditions of operationrtogether with a change in grinding wheel sizes. Also the amplitude of the oscillatory swing may be greatly varied and the opposite outwardly end units may be made to ride over or E the edge portions of the marble slab and need not necessarily be limited to action within the physical contines of the slab material. And further, while each head assembly is an integral and complete unit, the direction of rotation of the grinding wheels may be in either direction as may be brought about through reversible motors or by other suitable reversible drive means. Thus, every other spindle may be made to drive in an opposite direction from its next adjacent spindles to produce alternate reverse actuation of the grinding wheels.

Under the reversible drive conditions noted, it is also possible to have the two left hand spindles in Fig. 2 driven in one direction, While the two right hand spindles are driven in the opposite direction. With such selective rotational benefits of a battery of grinding spindles, it is possible to provide better control of the dust and loose slab material and/ or fluid and accompanying water employed in the grinding operation as well as to obtain the most beneficial nal results on slabs of various materials that are fed into the machine for surface grinding and/or polishing to a given predetermined surface condition.

One of the chief advantages of the opposite or counterrotation of the spindles and their associated grinding heads relates directly to the obtainment of a simple true and accurate rectilinear feed of the slab material that is being surface finished. A single rotating spindle, or a number of spindles all rotating in one direction, will impart a side thrust against the slab material to urge the slab out of its intended path of operation. Some of the machines now in use having single heads actually resort to clamping the slab in a guided frame to prevent the slab from being thrown out of the machine.

Thus with the selected counter-rotation of the spindles and grinding wheels as shown by the arrows in Fig. 3, as one example, the side thrust upon the surface of the fragmentarily shown slab is substantially nullitied and eliminated. The slab can be fed over the rollers under its own weight along a true course under the grinding mechanisms without the use of guiding and/or clamping means.

Referring to Figs. 1, 2 and 3 of the drawings, the various coacting mechanisms of the machine are all carried upon a framework 1 supported upon a rigid frame base 2, with both units 1 and 2 including suitable vertical, horizontal and diagonal structural members to create a solid and sturdy machine frame to support the coacting mechanisms of the slab surfacing machine,

A plurality of rollers 3 are iournalled in bearings 4 and 5 carried upon frame sides 6 and 7 to create a slab supporting bed or reactionary structure to support the work pieces such as marble slabs or the like at a given and fixed elevation as determined by the upper peripheral circumferential surface limits of the multiple rollers. The rollers 3 are normally all equidistant from each other as best shown in Figs. 1 and 3 with the exception of certain rollers 8 and 9 that underly the locations of the grinding spindles and the superimposed grinding areas of the slab.

All rollers are positively driven to provide the feed mechanism to advance a marble slab such as 10 under its own weight over the machine bed in edgewise relation at a given elevation and toward the grinding wheels of the spindles. In this connection it might be emphasized that the rollers are constructed of a material having good frictional characteristics to readily grip the underside of a slab and to advance the slab in a straight line in a rectilinear direction along the length of the machine and over the bed. The rollers may, for example, be made of a rubber or rubber composition material of very limited resiliency but having good frictional surfaces.

The roller drive is initiated from a motor 11 driving its motor shaft 12 that is connected with shaft 13 through a coupling 14. Shaft 13 is an inclusive driven part of a variable speed transmission 15 that drives a chain sprocket wheel I6 by means of the transmission shaft 17.

A chain 18 connects a sprocket wheel 19 with wheel 16, the sprocket wheel 19 being secured to the roller shaft 20 of the roller 9. The drive to the other rollers is then suitably transmitted by means of the laterally and alternately offset chain drives 21 and 22 that are actuated by suitable sprockets connected with the opposite end of the shaft of roller 9 as best seen in Fig. 3. Additionally alternately staggered chain drives 23 and 24 are employed to continue the positive drive to the other rollers 3 of the machine in the manner also best illustrated in Fig. 3.

With this arrangement, the motor 11 drives al1 of the rollers in concerted and positive manner. Motor 11 may be reversible, if desired, should rectilinear oscillation of a slab be needed or required under certain conditions of usage or operation. With the variable speed transmission 15, the roller speeds can be changed to vary the rate of slab feed.

The grinding apparatus is best illustrated generally at Z5 in Figs. l, 2 and 3, and this apparatus is equipped with multiple grinding heads such as 26, 27, 28 and 29 all supported in an overhead box frame 30. Frame 30 is provided with vertically spaced supporting ears or arms 31- 31 and 32-32 at its ends and vertically arranged pivot shafts 33 and 34 connect the respective ears with equal length sets of supporting arms 35-35 and 36-36. The sets of arms 35--35 and 36-36 are mounted in fixed relation upon respective pivot shafts 37 and 38 that are journalled in vertical positions in a tubular cross frame 39 attached at its ends with parallel and vertically positioned supporting sleeves or tubes 40 and 41 that operatively telescope into coacting orientation and guide sleeves or tubes 42 and 43. The sleeves 42 and 43 are stationarily secured in outboard relation upon vertically spaced frame parts such as parts 44 and 45 for tube 42, parts 46 and 47 for the tube 43, such frame parts including other suitable structural elements for stabilization and rigidity.

Referring now to Figs. l and 3, it should be noted that the sets of arms 35--35 and 36-36 provide means where by the box frame 3), together with the associated heads are adapted for bodily oscillation in an arc transversely of the machine over and across the path of advance of a work piece or slab that is carried upon the machine roller bed. Box frame 30 moves at right angles to the slab direction, as a unit, and the heads 26 to 29 describe individual arcs within the limits of their amplitude of oscillation. The general action may be well understood with reference to the diagrammatical layout appearing in Fig. 7.

A drive mechanism 48 provides the actuating means for the controlled oscillation of the grinding apparatus 25 and comprises a motor 49 mounted upon a platform 50 secured to the cross frame 39, the motor driving a pulley 51 having a transmission chain or belt 52 that rotates the belt wheel or pulley S3 of a speed reducing transmission 54. Transmission 54 includes a vertical drive shaft 55 that has a crank disc 56 to pivotally receive one end of a crank 57. The connection between members 56 and 57 is made by means of a suitable drive pin 58 that may be connected through any one of a number of openings 59 that are located about the disc 56 and on different radii with respect to the axis of rotation of the disc. This is done for purposes of varying the amplitude of the stroke of the crank 57 according to the opening selected to receive the crank drive pin 58.

The other end of the crank 57 is swingably secured for partial segmental actuation by means of a spindle or pin 60 that is carried by the outer end of an arm 61 which is connected with the grinding apparatus 25. Arm 61 preferably comprises a contiguous extension or integral part of one of the arms 32. Thus the oscillatory actuation of the grinding apparatus 25 is under the full control of the actuating mechanism 48 that is powered by the motor 49. With the cooperative action of the speed selections possible with the selective speed transmission 54 and with the stroke adjustment provided by the openings 59 in disc S6, considerable variation in the action of the grinding apparatus is possible whereby to obtain thedesired results to meet conditions to best suit the work piece characteristics and to establish a satisfactory iinal surface finish upon the slab being worked.

The more specific details of construction of each of the grinding heads 26 to 29 per se may best be seen' by reference to Figs. 4 to 6. Each grinding head comprises a motor 62 mounted upon an Yannular table or open center base 63 supported by a sleeve 64 secured to a structural division plate 65. A circular sleeve 66 is attached in depending relation to plate 65 and extends in vertically guided relation through upper and lower aligned openings 67 and 68 formed through the top and bottom Walls of the box frame 30. Motor 62 furnishes the power for driving the grinding wheel 69 associated with the head structure described. Power is transmitted through the motor shaft 70 into a coupling 71 that is connected with the adjacent end 72 of a power transmission shaft 73. Shaft 73 is journalled in upper and lower aligned bearings 74 and 75 which are respectively mounted upon plate 65' and upon the lower end of the sleeve 66. The lower end 76Vof shaft 73 is secured or otherwise suitably keyed to a drive mandrel or fixture 77 and the latter is held in place upon shaft 76 by` means of a lock nut 78. An annular plate 79 is mounted upon the lower face of the mandrel 77 with nuts 80 and plate 79 includes a downwardly directed peripheral ring 81 to orient and receive grinding wheel segments 82 that carry pairs of arcuately formed segmental diamond strips 83 and 84. Each of the segments 82 are suitably secured to the plate 79 by means of nuts 85.

Attention is also directed to the beveled bottom outer edge or face v86 that is provided on each segment 82 to dispose its radially outer strip 83 in a canted relation with respect to the strip 84 whereby a beveled cut is edgewise made into the surface area of a slab to be automatically followed by a sizing or inal dimensional cut by the non-beveled diamond strip 84 located on the face of its segment 82. Suitable radial sweeper segments may be employed on the segments with the strips 83 and 84 to assistin cleaning up the slabs.

` yEach grinding'wheel assembly includes an open top annular hood structure .or shield 87 bolted to the top side of plate v79 and formed to surround the conical exterior 88 of the mandrel 77. Plate 79 is provided with openings 89 that communicatewith the chamber 90 defined by the shield 87 and mandrel 77. The openings 89 are each enlarged downwardly to aid in drawing the water down from chamber 90 into the diamond cutting area or zone underjoperation of the grinding heads.

A suitable Water supply conduit 91 is carried by the box frame 30 to direct water supplied through a hose 92 into the chamber 90 to supply Water through openings 89 to the grinding zone on the slab. Various other supported dust and iiuid shields such as 93 in Fig. 2 may be used to conne and localize a good deal of the free mixture of marble or slab dust and Water that surrounds the grinding wheel locations. Suitable trough means such as 94 are further employed beneath the grinding areas for the collection of free materials coming from the grinding wheels.

One of the further advantageous arrangements embodied in the grinding machine has to do with the matter of positive vertical adjustmentk of the grinding heads 26 to 29. It is important to initially establish a good horizontal alignment of the grinding wheel faces of the multiple heads. Since each head is oriented and vertically guidableby means of the sleeve 66 riding within the box frame openings 67 and 68, a fine adjustable abutment unit or stop means such as 95 is connected with each head assembly for vertical Vorientation of the head in relation to the box frame 30 and to prevent rotation of the head relative to the frame 30. 'Ihe abutment unit and adjusting means 95 comprises a threaded upright stud 96 loosely positioned Within an opening 97 formed in an orientation element or ear 98 on plate 65 with opposite outward nuts 99 and 100 providing regulatory'meansas instru-v mentalities to positively fix the position of the plate, '65 relatively to the stud 96. Stud 96 is rigidly Supported with its end 101 ixedly connected with a plate 102 that is secured to the top of the box frame 30 as best illustrated in Fig. 4. Vertical adjustment in small increments is readily possible with the adjustable abutment stop means such as to thus provide a manual adjustment for the vertical positional regulation of the associated head in relation to the supporting frame 30.

Supplementing the above described adjustment is the larger and more comprehensive mechanismV that bodily elevates or lowers the entire grinding head apparatus relatively to the slab carrying roller bed used to feed a slab material along the machine. This latter overall vertical adjusting mechanism is best shown in Figs. l and 2. This adjusting means is a power driven apparatus that may be controlled for given height changes or variations by on and olf energizations ofthe motor for selected intervals or under conventional limit controls.

The head assembly elevating apparatus comprises a selectively reversible motor 103 having a belt drive 104 to drive a transverse cross shaft 105 that connects with speed reducing transmissions 106 and 107 through suitable couplings 108 and 109. Each transmission is provided with a drive shaft such as 110 and 111 respectively that drive chain or belt means 112 and 113 to rotate vertical jack screws such as 114 and 115 that are'located on the axial centers of the telescopic means `l0- d2 and 41-43 described to support the grinding heads. Screws 114 and 115 operate through orientation bushings 11'6 and 117 carried upon frame parts 45 and 47 to hold the screws against endwise vertical displacement. The upper free ends of screws 114 and 115 thread through nuts 118 and 119-secured to the lower ends of the sleeves 40 and 41 as seen'in Fig. 2.

By energizing motor 103, the drive is completed by the mechanism described to the jack screws 114 and 115 which will draw the nuts 118 or 119 upwardly or downwardly according tothe direction of operative rotation of the motor 103. This will produce relative motion between the sleeve sets t0-42 and 41--43 to change or regulate the elevation of the box frame 30 and the supported grinding heads 26 to 29 carried by such overhead frame 30 and 40-'41, the latter units together forming a U-frame structure.

From the above description it will be apparent that the slab surfacing machine provides a grinding or lnishing structure that edgewise removes a complete surface increment of material from a rough cut slab oriented in a given supported relation to the grinding structure. This action is well illustrated in Fig. 4 wherein a slab of material is being advanced in the direction of the arrow and a grinding wheel is disposed in a given relation in the path of the slab toedgewise cut into and across the top face of the slab in a coplanar manner to establish a smooth, true and level finished surface along a division line on the slab.

Fig. 7 is used to further show how the grinding wheels are arcuately oscillated in paths transversely related to the rectilinear path of travel of a slab, the oscillations of the wheels having amplitudes to cause overlapped cuttings. The cuttings are made convexly directed againstthe path of the slab advance to thus obtain continuous compound motion of arcuate sawtooth cuttings across the slab face by each of the grinding instrumentalities.

The foregoing description relates to one preferred embodiment of the invention. Certain changes in the combinations and in the individual elements thereof areV contemplated without departing from the fundamental coricept of the invention herein disclosed. The extent of such modifications shall, however, be governed by the breadth and scope of the appended claimed subject matter directed to a slab surfacing machine of the present invention.

What I claim is:

1. In a nishing machine for slab materials comprising a feed mechanism to actuate a slab along a given path of operation, grinding units to engage an approaching edge of said slab each comprising a housing structure to support a power unit, a grinding wheel having circumferentially located grinding members thereabout, and a means to connect said power unit to drive said wheel, and a frame Structure to collectively support said grinding units in a given relation to position said grinding members of the wheels directly within the path of the advancing edge of said slab to edgewise cut into the slab, said frame including adjustable guide means to movably carry all of the grinding units toward or away from the slab path, and adjustable mechanisms each interposed between the individual housing structures of said grinding units respectively and said frame structure to independently fix the position of the separate grinding members of the grinding units in a given relation with respect to the frame and to the path of travel of said slab, said adjustable mechanisms each comprising an orientation element integrally carried by one of said structures, together with regulatory means on the other of said structures connected to shift said orientation element into selected fixed positions.

2. In a finishing machine as in claim 1, wherein independent synchronized elevating and lowering mechanisms are connected with said adjustable guide means of said frame structure to selectively orient all of said grinding members of the grinding units in a given intercepting elevation with respect to the path of movement of said slab.

3. In a finishing machine as in claim l, wherein oscillatory mechanism is interposed between said frame structure and said grinding units to bodily actuate all of said grinding units and their connected grinding wheel grinding members along given paths described transversely to the movement of said slab.

4. In a finishing machine as in claim 3, wherein said grinding wheels are closely spaced to provide overlapping oscillatory action to cause said grinding members of the wheels to duplicate the grinding operation across predetermined common areas of the slab surfaces being worked by said machine.

5. ln a hard slab surface truing machine comprising, in combination, means to orient and to actuate a slab in a given direction along a horizontal plane of operation, and a plurality of grinding heads having grinding wheels provided with marginal cutting instrumentalities to horizontally engage and to cut away a surface portion of said slab, and swingable mechanism to bodily support said grinding heads comprising means to oscillate each of said grinding heads coincidentally with and along said same given plane of operation of said slab, said swingable mechanism functioning to oscillate said heads in parallel relation through individual arcs traversing portions below the original surface of said slab.

6. In a hard slab finishing machine as in claim 5, wherein said grinding wheels of said heads are closely spaced with respect to each other whereby said cutting instrumentalities of said wheels operate in overlapping arcuate patterns to duplicate the grinding action in alternate opposite directions over certain predetermined areas below the original surface of said slab.

7. A slab surfacing machine comprising a feed mechanism providing multiple supporting and actuating means to engage the under face of a slab and to feed said slab edgewise along a fixed path, grinding mechanisms including finishing wheels having radially outer marginally connected cutting instrumentalities thereabout arranged for peripheral contact and for disposition in the path of travel of said slab, said finishing wheels each occupying a common elevation to dispose said cutting instrumentalities in a predetermined cutting plane of operation to edgewise intercept an edge of said slab along a reference plane bearing a given elevated relation with respect to the supported underface of the slab, and adjustable gauge means carrying said grinding mechanisms to regulate the maximum predetermined downward positions of said finishing wheels in relation to the slab to edgewise engage and to remove a complete surface layer of material from said slab along a true and continuous single surface coincident with said reference plane While said slab is edgewise actuated along said fixed path against the peripheries of and beyond the locations of said finishing wheels by said feed mechanism.

8. In a hard slab finishing machine comprising, in combination, means to actuate a slab in a given direction along a predetermined plane, and a plurality of grinding heads having grinding wheels adapted for coplanar operation to engage and to nish a surface portion of said slab, and swingable mechanism to support all of said grinding heads comprising means to oscillate each of said grinding heads along the general plane of operation of said slab and in individual arcs traversing fractional portions of the surface of the total width of said slab, and power means to drive said swingable mechanism comprising a motor, a rotary disc, drive means actuated by said motor and connected to drive said disc, and a crank on said disc connected to operate said swingable mechanism.

9. In a hard slab finishing machine comprising, in combination, means to actuate a slab in a given direction along a predetermined plane, and a plurality of grinding heads having grinding wheels adapted for coplanar operation to engage and to finish a surface portion of said slab, and swingable mechanism to support all of said grinding heads comprising means to oscillate each of said grinding heads along the general plane of operation of said slab and in individual arcs traversing fractional portions of the surface of the total width of said slab, and power means to drive said swingable mechanism comprising a motor, a rotary disc, drive means actuated by said motor and connected to drive said disc, a crank on said disc connected to operate said swingable mechanism, and releasable pivotal means to connect said crank with said disc, said pivotal means being carried in an opening in the disc, said disc opening being located at a given radius with respect to the axis of rotation of said disc and said disc being provided with other openings located at different radial distances from the axis of rotation of the disc to interchangeably receive said pivotal means to thereby selectively vary the crank throw and the amplitude of the arcs of oscillation of the grinding heads.

l0. In a hard slab finishing machine comprising, in combination, means to actuate a slab in a given direction along a predetermined plane, and a plurality of grinding heads having grinding wheels adapted for coplanar operation to engage and to finish a surface portion of said slab, and swingable mechanism to support all of said grinding heads comprising means to oscillate each of said grinding heads along the general plane of operation of said slab and in individual arcs traversing fractional portions of the surface of the total width of said slab, and power means to drive said swingable mechanism comprising a motor, a rotary disc, drive means actuated by said motor and connected to drive said disc, and a crank on said disc connected to operate said swingable mechanism, said swingable mechanism having extensible mechanism connected therewith to selectively regulate the positions of the grinding wheels of said grinding heads in a direction normal to the plane of operation of the slab.

ll. The method of finish cutting at least one face of a rought cut slab of hard material having surface undulations and rough areas thereon primarily as a result of the rough cutting thereof, whereby said finish cut establishes a smooth, true, and coplanar level surface on said one face of the slab, which comprises orienting said slab of material to stabilize and to support said one face thereof at a predetermined elevation, providing a cutting instrumentality to engage the slab for translatory coplanar grinding along a reference plane occupying a given maximum position beneath the general exterior surface plane of the face of the slab with said reference plane occupying a position to include all of the undulations and rough areas of the one face of the slab, and causing relative intercepting bodily movement between the grinding instrumentality and said slab along said reference plane to completely eliminate the material of the slab above said reference plane including all the undulations and rough areas appearing on the slab face being processed.

12. The method of providing a smooth, true, and coplanar level surface upon at least one face of a rough cut slab of hard material having surface undulations and rough areas on said one face, which comprises orienting said slab of material to stabilize and to support said one face thereof for movement in the direction of the general plane of the slab, providing a cutting instrumentality directly in the path of movement of said slab for bodily contact and coplanar grinding along a reference plane occupying a given maximum position with respect to the thickness of the slab with the reference plane bear ing a predetermined vertical relation with respect to the exterior limits of the face being processed to include all of the undulations and rough areas of the one face within the path of action of said cutting instrumentality, and causing relative bodily motion between said slab and said grinding instrumentality along the general plane of the slab and in a continuous advancing direction along the reference plane to completely remove all of the material of the slab along said one face including all undulations and rough areas appearing on said slab face.

13. The method of finish cutting at least one face of a rough cut slab of hard material having surface undulations and rough areas thereon primarily as a result of the rough cutting thereof, whereby said finish cut establishes a smooth, true, and coplanar level surface on said one face of the slab, which comprises orienting said slab of material to stabilize and to support said one face thereof at a predetermined elevation, providing a cutting instrumentality to engage the slab for translatory coplanar grinding along a reference plane occupying a given maximum position beneath the general exterior surface plane of the face of the slab with said reference plane occupying a position to include all of the undulations and rough areas of the one face of the slab, and uniformly actuating said slab of material in a continuous rectilinear direction along the reference plane to intercept said grinding instrumentality while causing said grinding instrumentality to arcuately oscillate transversely to the path of movement of said slab for convex removal of the material of the slab above said reference plane including all of the undulations and rough areas appearing on the slab face being processed.

14. In the method of claim 13 with the use of a number of grinding instrumentalities to provide multiple arcuate cuttings on the slab and wherein said grinding instrumentalities are arcuately oscillated to provide adjacently overlapping cuttings of the slab material coincidently with the reference plane of the slab.

15. In the method of claim 13 which includes a grinding instrumentality providing coacting multiple cutting facilities to cause said convex removal of the slab material along the reference plane and to simultaneously surface nish the newly established true and level slab face remaining in the wake of the convex material removal of the slab undulations and rough areas.

16. A machine for surface cutting and surface truing a rough cut slab of hard material having exterior surface undulations and rough areas thereon comprising mechanism to support and to orienta slab in a given plane, and grinding apparatus disposed in a predetermined relation with respect to said slab comprising a frame structure carrying a plurality of grinding heads thereon, said heads each comprising a housing structure, a power unit, a grinding wheel, rotary means connected to support said grinding wheels for operation in a xed plane with respect to said housing structure and in relation to the oriented slab, and drive means connected between said motor and the rotary means, said frame structure incorporating guide means to slidably accommodate the housing structures of each head for movement toward or away from the slab plane, and independent adjustable abutment means for each head interposed between the housing structure of the head and said'frame structure to bodily support said head to orient its grinding wheel in a given vertical relation with respect to the slab, said grinding wheel having circumferentially arranged grinding elements for disposition below the upper surface level of the slab to a point coincident with a reference plane including all of the slab undulations and rough areas, and apparatus connected to cause relative movement between said slab and said heads to actuate the circumferential grinding elements of the grinding wheels against and into a peripheral edge of said slab to remove all of the slab material lying above said reference plane to establish a smooth coplanar surface upon the slab.

17. In a machine as in claim 16 wherein said frame structure is supported upon vertically cooperative telescoping members to bodily elevate or lower the entire grinding apparatus relatively to the plane of the slab.

18. In a machine as in claim 16, with the addition of extensible means that are connected with said frame structure for the bodily elevation or lowering the entire grinding apparatus with respect to the oriented position of the slab.

19. In the combination of claim 16, with the addition of cooperative extensible means connected at spaced points f on said frame structure to bodily elevate or bodily lower the entire grinding apparatus with respect to the oriented position of the slab, and power operated means including synchronized screw members are connected to actuate said cooperative extensible means in unison.

20. A mechanism for providing a smooth and true coplanar surface on at least one face of a rough cut slab of hard material having undulations and rough areas on said one face, comprising, in combination, supporting means to orient said slab with its one face located at a given elevation, a grinding unit having a wheel including coacting cutting instrumentalities located in angular relation with respect to each other adapted for removal of slab material along a horizontal reference plane, means to adjust said grinding unit for operation coincident with said reference plane, the location of said reference plane being vertically inwardly from the general exterior surface of the one slab face an amount to include all of said undulations and rough areas, and apparatus to cause relative movement between said grinding unit and said slab to cause said unit to remove slab material from along the reference plane, certain of said cutting instrumentalities functioning to cut way slab material from above said reference plane and certain other of said cutting instrumentalities functioning to nish the newly developed coplanar surface on said one face of the slab.

21. In a mechanism `as in claim 20, with the addition of laterally swingable supporting means to carry said grinding unit and power mechanism to actuate said swingable means in oscillatory fashion across said slab, and wherein said apparatus causing relative movement between said grinding unit and said slab actuates the latter along a rectilinear path under said swinging grinding unit.

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